The technology of the disclosure relates generally to signal generation, and in particular to providing devices, systems, and methods to generate sinusoidal signals.
A sinusoidal signal is a signal that oscillates between a high and low value in a sine or cosine shaped waveform. Sinusoidal signals are frequently used to represent physical phenomenon such as the movement of a weight on a spring or the shape of a sound wave. Sinusoidal signals are also commonly used in electronic applications such as power transmission (AC current) and communications. In electronic systems, a sinusoidal signal generator can be employed to generate a sinusoidal signal.
A common approach to generating a sinusoidal signal is to use a Pulse Width Modulation (PWM) signal. The PWM signal can be filtered through a band-pass filter or low-pass filter to create a sinusoidal signal. This is illustrated by example in the sinusoidal signal generator 10 in FIG. 1. As illustrated in FIG. 1, the sinusoidal signal generator includes a circuit 12 that is configured to generate a PWM signal 14. An example of the PWM signal 14 is illustrated in FIG. 2A. The PWM signal 14 is input into a band-pass filter 16 that generates a resulting sinusoidal signal 18 on filter output 20. The PWM signal 14 provides frequency and amplitude control of the sinusoidal signal 18. The frequency of the generated sinusoidal signal 18 is the frequency of the PWM signal 14. The frequency of the PWM signal 14 is the frequency of alternations between an inactive state and an active state. In the PWM signal 14, the inactive state is a low signal level and the active state is a high signal level. This combination is referred to as a low-to-high PWM signal. In a high-to-low PWM signal, the inactive state is a high signal level and the active state is a low signal level. When the signal level is in the active state, pulses 22 are generated in the PWM signal 14, as illustrated in FIG. 2A. The amplitude of the generated sinusoidal signal 18 is controlled by the duty cycle of the PWM signal 14, as illustrated in FIG. 2B. The duty cycle of the PWM signal 14 is the percentage of time that a pulse 22 appears in a given period T of a PWM signal 14. The direct current (DC) offset 24 of the sinusoidal signal 18 in FIG. 2B is the average value of the PWM signal 14 in FIG. 2A. In other words, the DC offset 24 of the sinusoidal signal 18 is equal to INACTIVE+D(ACTIVE−INACTIVE), where ACTIVE and INACTIVE are the signal levels corresponding to the active state and the inactive state of the PWM signal 14, respectively, and D is the duty cycle of the PWM signal 14.
There are many applications which require a sinusoidal signal that has an amplitude gradually changing from a zero signal level to some maximal signal level and then back to a zero signal level. One example of such application is ultrasonic localization. In ultrasonic localization applications, beacons may be placed in various locations and emit an ultrasonic sound wave, such as by wireless transmission of the generated sinusoidal signal 18 over speaker 26 as wireless generated sinusoidal signal 18′, as shown in FIG. 1. An electronic device may determine its location by receiving these sound signals, such as the wireless generated sinusoidal signal 18′ received through a microphone 27 in FIG. 1, and performing time of flight calculations. The ultrasound localization beacons may transmit a sinusoidal signal that has an amplitude gradually changing from a zero signal level to some maximal signal level and then back to a zero signal level.
Thus, with reference back to FIG. 2B, if it is desired to vary the amplitude of the sinusoidal signal 18 from a zero signal level 0 to a desired maximal signal level M, and then back to the zero signal level 0, the duty cycle of the PWM signal 14 in FIG. 2A should be controlled to vary from a zero duty cycle to a desired maximal duty cycle (e.g., 50%) and then back to a zero duty cycle. This creates a DC offset 24 that starts at low level and gradually increases while the duty cycle of the PWM signal 14 increases. This variation in the DC offset 24 creates distortion in the sinusoidal signal 18 that can cause distortion in other components of a system employing the sinusoidal signal 18.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.